ELECTROMAGNETIC-FIELDS OF SURFACE COIL INVIVO NMR AT HIGH-FREQUENCIES
ELECTROMAGNETIC-FIELDS OF SURFACE COIL INVIVO NMR AT HIGH-FREQUENCIES
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DOI：
10.1002/mrm.1910220254
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发表时间：
1991-12-01
影响因子：
3.3
通讯作者：
BUDINGER, TF
中科院分区：
文献类型：
--
作者：
KELTNER, JR;CARLSON, JW;BUDINGER, TF
A high frequency solution of the electromagnetic field produced by a circular surface coil adjacend to a homogenous conducting, dielectric sphere is used to predict the attainable signal to noise ratio (S/N) and specific absorption rate (SAR) forin vivo1H NMR spec troscopy experiments from 200 to 430 MHz (4.7–10T). Above 200 MHz theS/Nincreases more rapidly with frequency and the SAR increases less rapidly compared with the respectiveS/Nand SAR frequency dependence below 200 MHz. The difference in frequency dependence is due to dielectric resonances of the magnetic field inside the sphere at frequencies above 200 MHz. It is predicted that surface coil1H NMR experiments may be performed on a head‐sized sphere, having conductivity and relative dielectric constant of brain, at frequencies up to 430 MHz without exceeding 8 W/kg local SAR and 3.2 W/kg SAR. The calculations of theS/Nand SAR are used to determine optimum surface coil geometries for NMR experments. The power radited by the surface coil in the absence of shielding and asymmetries in the received signal with respect to the plane defined by the surface coil axix and the direction of the static magnetic field are significant at high frequency. Experimental measurements of the magnetic field inside a head‐sized sphere verfy the presence of dielectric resonances at frequencies above 200 MHz. © 1991 Academic Press, Inc.
